Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, yellow, blue, and cream. The most popular category of koi is the Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.

Contents

Carp are a large group of fish originally found in Central Europe and Asia. Various carp species were originally domesticated in East Asia, where they were used as food fish. Carp are coldwater fish, and their ability to survive and adapt to many climates and water conditions allowed the domesticated species to be propagated to many new locations, including Japan. Natural color mutations of these carp would have occurred across all populations. Carp were first bred for color mutations in China more than a thousand years ago, where selective breeding of the Prussian carp (Carassius gibelio) led to the development of the goldfish.[2]

The common carp were aquacultured as a food fish at least as long ago as the fifth century BC in China, and in the Roman Empire during the spread of Christianity in Europe.[3] Common carp were bred for color in Japan in the 1820s, initially in the town of Ojiya in the Niigata prefecture on the northeastern coast of Honshu island. By the 20th century, a number of color patterns had been established, most notably the red-and-white Kohaku.

The outside world was not aware of the development of color variations in Japanese koi until 1914, when the Niigata koi were exhibited at an annual exposition in Tokyo. From that time, interest in koi spread throughout Japan. It was from this original handful of koi that all other Nishikigoi varieties were bred, with the exception of the Ogon variety (single colored, metallic koi) which was developed relatively recently. The hobby of keeping koi eventually spread worldwide. Koi are now sold in many pet aquarium shops, with higher-quality fish available from specialist dealers.[4][5]

Extensive hybridization between different populations coupled with widespread translocations have muddled the historical zoogeography of the common carp (C. carpio) and its relatives. Traditionally, East Asian carp were included as a subspecies of the common carp under the scientific name C. carpio haematopterus.[6] These differ in meristics from the common carp of Europe and Western Asia,[7] leading recent authorities to recognize them as a separate species, C. rubrofuscus (haematopterus being a junior synonym).[8][9] Although one study of mitochondrial DNA (mtDNA) was unable to find a clear genetic structure matching the geographic populations (possibly because of translocation of carps from separate regions),[10] others based on mtDNA, microsatellite DNA and genomic DNA found a clear separation between the European/West Asian population and the East Asian population, with koi belonging in the latter.[6][11][12] Consequently, recent authorities have suggested that the ancestral species of the koi is C. rubrofuscus (syn.C. c. haematopterus) or at least an East Asian carp species instead of C. carpio.[7][13] Regardless, a taxonomic review of Cyprinus carp from eastern and southeastern Asia may be necessary as the genetic variations do not fully match the currently recognized species pattern,[11] with one study of mtDNA suggesting that koi are close to the southeast Asian carp, but not necessarily the Chinese.[14]

The word koi comes from Japanese, simply meaning "carp." It includes both the dull grey fish and the brightly colored varieties. What are known as koi in English are referred to more specifically as nishikigoi in Japan (literally meaning "brocaded carp"). In Japanese, koi is a homophone for another word that means "affection" or "love"; koi are therefore symbols of love and friendship in Japan.

Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, yellow, blue, and cream. While the possible colors are virtually limitless, breeders have identified and named a number of specific categories. The most notable category is Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.

New koi varieties are still being actively developed.[15] Ghost koi developed in the 1980s have become very popular in the United Kingdom; they are a hybrid of wild carp and Ogon koi, and are distinguished by their metallic scales. Butterfly koi (also known as longfin koi, or dragon carp), also developed in the 1980s, are notable for their long and flowing fins. They are hybrids of koi with Asian carp. Butterfly koi and ghost koi are considered by some to be not true nishikigoi.[citation needed]

The major named varieties include:

Kohaku

Taisho Sanke

Showa Sanke

Tanchō

Chagoi

Asagi

Utsurimono

Bekko

Goshiki

Shūsui

Kinginrin

Kawarimono

Ōgon

Kumonryū

Ochiba

Koromo

Hikari-moyomono

Kikokuryū

Kin-Kikokuryū

Ghost koi

Butterfly koi

Doitsu-goi

Kōhaku(紅白?) is a white-skinned koi, with large red markings on the top. The name means "red and white"; kohaku was the first ornamental variety to be established in Japan (late 19th century).[16]

Taishō Sanshoku (or Taisho Sanke)(大正三色?) is very similar to the kohaku, except for the addition of small black markings called sumi(墨?). This variety was first exhibited in 1914 by the koi breeder Gonzo Hiroi, during the reign of the Taisho Emperor.[citation needed] In America, the name is often abbreviated to just "Sanke." The kanji, 三色, may be read as either sanshoku or as sanke (from its earlier name 三毛).

Shōwa Sanshoku (or Showa Sanke) (昭和三色?) is a black koi with red (hi 緋) and white (shiroji 白地) markings. The first Showa Sanke was exhibited in 1927, during the reign of the Showa Emperor. In America, the name is often abbreviated to just "Showa." The amount of shiroji on Showa Sanke has increased in modern times (Kindai Showa 近代昭和), to the point that it can be difficult to distinguish from Taisho Sanke. The kanji, 三色, may be read as either sanshoku or as sanke.

Tanchō(丹頂?) is any koi with a solitary red patch on its head. The fish may be a Tancho Showa, Tancho Sanke, or even Tancho Goshiki. It is named for the Japanese crane (Grus japonensis), which also has a red spot on its head.

Chagoi(茶鯉?), "tea-colored," this koi can range in color from pale olive-drab green or brown to copper or bronze and more recently, darker, subdued orange shades. Famous for its docile, friendly personality and large size, it is considered a sign of good luck among koi keepers.

Asagi(浅黄?) koi is light blue above and usually red below, but also occasionally pale yellow or cream, generally below the lateral line and on the cheeks. The Japanese name means pale greenish-blue, spring onion color, or indigo.

Utsurimono(写り物?) is a black koi with a white, red, or yellow markings, in a zebra color pattern. The oldest attested form is the yellow form, called "black and yellow markings" (黒黄斑,Kuro ki madara?) in the 19th century, but renamed Ki Utsuri(黄写り?) by Elizaburo Hoshino, an early 20th-century koi breeder. The red and white versions are called Hi Utsuri(緋写り?) and Shiro Utsuri(白写り?) (piebald color morph), respectively. The word utsuri means to print (the black markings are reminiscent of ink stains). Genetically, it is the same as Showa, but lacking either red pigment (Shiro Utsuri) or white pigment (Hi Utsuri/Ki Utsuri).

Bekko(べっ甲?) is a white-, red-, or yellow-skinned koi with black markings sumi(墨?). The Japanese name means "tortoise shell," and is commonly written as べっ甲. The white, red, and yellow varieties are called Shiro Bekko(白?), Aka Bekko(赤?) and Ki Bekko(黄?), respectively. It may be confused with the Utsuri.

Goshiki(五色?) is a dark koi with red (Kohaku style) hi pattern. The Japanese name means "five colors." It appears similar to an Asagi, with little or no hi below the lateral line and a Kohaku Hi pattern over reticulated (fishnet pattern) scales. The base color can range from nearly black to very pale, sky blue.

Shūsui(秋翠?) means "autumn green"; the Shūsui was created in 1910 by Yoshigoro Akiyama（秋山 吉五郎, by crossing Japanese Asagi with German mirror carp.[citation needed] The fish has no scales, except for a single line of large mirror scales dorsally, extending from head to tail. The most common type of Shūsui have a pale, sky-blue/gray color above the lateral line and red or orange (and very, very rarely bright yellow) below the lateral line and on the cheeks.

Kinginrin(金銀鱗?) is a koi with metallic (glittering, metal-flake-appearing) scales. The name translates into English as "gold and silver scales"; it is often abbreviated to Ginrin. There are Ginrin versions of almost all other varieties of koi, and they are fashionable. Their sparkling, glittering scales contrast to the smooth, even, metallic skin and scales seen in the Ogon varieties. Recently, these characteristics have been combined to create the new ginrin Ogon varieties.

Kawarimono(変わり物?) is a "catch-all" term for koi that cannot be put into one of the other categories. This is a competition category, and many new varieties of koi compete in this one category. It is also known as kawarigoi(変わり鯉?).[citation needed]

Ōgon(黄金?) is a metallic koi of one color only (hikarimono 光者). The most commonly encountered colors are gold, platinum, and orange. Cream specimens are very rare. Ogon compete in the Kawarimono category and the Japanese name means "gold." The variety was created by Sawata Aoki in 1946 from wild carp he caught in 1921. Recently, the metallic-skinned Ogon is being crossed with ginrin-scaled fish to create the ginrin Ogon with metallic skin and sparkling (metal flake) scales.

Kumonryū(九紋竜?) （literally "nine tattooed dragons" is a black doitsu-scaled fish with curling white markings. The patterns are thought to be reminiscent of Japanese ink paintings of dragons. They famously change color with the seasons.[citation needed]Kumonryu compete in the Kawarimono category.

Ochiba(落葉?) is a light blue/gray koi with copper, bronze, or yellow (Kohaku-style) pattern, reminiscent of autumn leaves on water. The Japanese name means "fallen leaves."

Koromo(衣?) is a white fish with a Kohaku-style pattern with blue or black-edged scales only over the hi pattern. This variety first arose in the 1950s as a cross between a Kohaku and an Asagi.[citation needed] The most commonly encountered Koromo is an Ai Goromo, which is colored like a Kohaku, except each of the scales within the red patches has a blue or black edge to it. Less common is the Budo-Goromo, which has a darker (burgundy) hi overlay that gives it the appearance of bunches of grapes. Very rarely seen is the Tsumi-Goromo which is similar to Budo-Goromo, but the hi pattern is such a dark burgundy that it appears nearly black.

Hikari-moyomono(光模樣者?) is a koi with colored markings over a metallic base or in two metallic colors.

Kikokuryū（輝黒竜, literally "sparkle" or "glitter black dragon"）is a metallic-skinned version of the Kumonryu.

Kin-Kikokuryū （金輝黒竜, literally "gold sparkle black dragon" or "gold glitter black dragon"）is a metallic-skinned version of the Kumonryu with a Kohaku-style hi pattern developed by Mr. Seiki Igarashi of Ojiya City. There are (at least) six different genetic subvarieties of this general variety.

Ghost koi（人面魚、じんめんぎょ, a hybrid of Ogon and wild carp with metallic scales, is considered by some to be not nishikigoi.

Butterfly koi（鰭長錦鯉、ひれながにしきごい） is a hybrid of koi and Asian carp with long flowing fins. Various colorations depend on the koi stock used to cross. It also is considered by some to not be nishikigoi.

Doitsu-goi(ドイツ鯉?) originated by crossbreeding numerous different established varieties with "scaleless" German carp (generally, fish with only a single line of scales along each side of the dorsal fin). Also written as 独逸鯉, there are four main types of Doitsu scale patterns. The most common type (referred to above) has a row of scales beginning at the front of the dorsal fin and ending at the end of the dorsal fin (along both sides of the fin). The second type has a row of scales beginning where the head meets the shoulder and running the entire length of the fish (along both sides). The third type is the same as the second, with the addition of a line of (often quite large) scales running along the lateral line (along the side) of the fish, also referred to as "mirror koi." The fourth (and rarest) type is referred to as "armor koi" and are completely (or nearly) covered with very large scales that resemble plates of armor. They also are called Kagami-goi（鏡鯉、カガミゴイ, or mirror carp（ミラーカープ）

Koi have prominent barbels on the lip that are not visible in goldfish.

Goldfish were developed in China more than a thousand years ago by selectively breeding Prussian carp for color mutations. By the Song dynasty (960–1279), yellow, orange, white, and red-and-white colorations had been developed. Goldfish (Carassius auratus) and Prussian carp (Carassius gibelio) are now considered different species. Goldfish were introduced to Japan in the 16th century and to Europe in the 17th century.[2] Koi, on the other hand, were developed from common carp in Japan in the 1820s. Koi are domesticated common carp (Cyprinus carpio) that are selected or culled for color; they are not a different species but a subspecies, and will revert to the original coloration within a few generations if allowed to breed freely.

In general, goldfish tend to be smaller than koi, and have a greater variety of body shapes and fin and tail configurations. Koi varieties tend to have a common body shape, but have a greater variety of coloration and color patterns. They also have prominent barbels on the lip. Some goldfish varieties, such as the common goldfish, comet goldfish, and shubunkin have body shapes and coloration that are similar to koi, and can be difficult to tell apart from koi when immature. Since goldfish and koi were developed from different species of carp, even though they can interbreed, their offspring are sterile.[17][18]

The common carp is a hardy fish, and koi retain that durability. Koi are cold-water fish, but benefit from being kept in the 15–25 °C (59–77 °F) range, and do not react well to long, cold, winter temperatures; their immune systems are very weak below 10 °C. Koi ponds usually have a metre or more of depth in areas of the world that become warm during the summer, whereas in areas that have harsher winters, ponds generally have a minimum of 1.5 m (5 ft). Specific pond construction has been evolved by koi keepers intent on raising show-quality koi.

The bright colors of koi put them at a severe disadvantage against predators; a white-skinned Kohaku is a visual dinner bell against the dark green of a pond. Herons, kingfishers, otters, raccoons, cats, foxes, badgers and hedgehogs are all capable of emptying a pond of its fish. A well-designed outdoor pond will have areas too deep for herons to stand, overhangs high enough above the water that mammals cannot reach in, and shade trees overhead to block the view of aerial passers-by. It may prove necessary to string nets or wires above the surface. A pond usually includes a pump and filtration system to keep the water clear.

Koi are an omnivorous fish, and will eat a wide variety of foods, including peas, lettuce, and watermelon. Koi food is designed not only to be nutritionally balanced, but also to float so as to encourage them to come to the surface. When they are eating, it is possible to check koi for parasites and ulcers. Naturally koi are bottom feeders with a mouth configuration that is designed for that. Some koi will have a tendency to eat mostly from the bottom and therefore food producers will create a mixed sinking and floating combination food. Koi will recognize the persons feeding them and gather around them at feeding times. They can be trained to take food from one's hand. In the winter, their digestive systems slow nearly to a halt, and they eat very little, perhaps no more than nibbles of algae from the bottom. Feeding is not recommended when the water temperature drops below 10 °C (50 °F).[19][20] Care should be taken by hobbyists that proper oxygenation, ph stabilization and off-gassing occurs over the winter months in small water ponds, so they do not perish. Their appetites will not come back until the water becomes warm in the spring.

There are reports of kois that have achieved ages of 100–200 years.[21] One famous scarlet koi, named "Hanako," was owned by several individuals, the last of whom was Dr. Komei Koshihara. In July 1974, a study of the growth rings of one of the koi's scales reported that Hanako was 225 years old.[22] The greatest authoritatively accepted age for the species is little more than 50 years.[23][24]

Koi are very hardy. With proper care, they resist many of the parasites that affect more sensitive tropical fish species, such as Trichodina, Epistylis, Ich and other ciliated protozoans. Two of the biggest health concerns among koi breeders are the koi herpes virus (KHV) and rhabdovirus carpio, which causes spring viraemia of carp (SVC). No treatment exists for either disease. Some koi farms in Israel use the KV3 vaccine, developed by Prof. M. Kotler from the Hebrew University and produced by Kovax, to immunise fish against KHV. They are currently the only country in the world to vaccinate koi carp against the koi herpes virus. The vaccine is injected into the fish when they are under one year old, and is accentuated by using an ultraviolet light. The vaccine has a 90% success rate[25] and when immunised the fish cannot succumb to a KHV outbreak and neither can the immunised koi pass KHV onto other fish in a pond.[26] Only biosecurity measures such as prompt detection, isolation and disinfection of tanks and equipment can prevent the spread of the disease and limit the loss of fish stock. In 2002, spring viraemia struck an ornamental koi farm in Kernersville, North Carolina, and required complete depopulation of the ponds and a lengthy quarantine period. For a while after this, some koi farmers in neighbouring states stopped importing fish for fear of infecting their own stocks.[27][28]

Like most fish, koi reproduce through spawning in which a female lays a vast number of eggs and one or more males fertilize them. Nurturing the resulting offspring (referred to as "fry") is a tricky and tedious job, usually done only by professionals. Although a koi breeder may carefully select the parents they wish based on their desired characteristics, the resulting fry will nonetheless exhibit a wide range of color and quality.

Koi will produce thousands of offspring from a single spawning. However, unlike cattle, purebred dogs, or more relevantly, goldfish, the large majority of these offspring, even from the best champion-grade koi, will not be acceptable as nishikigoi (they have no interesting colors) or may even be genetically defective. These unacceptable offspring are culled at various stages of development based on the breeder's expert eye and closely guarded trade techniques. Culled fry are usually destroyed or used as feeder fish (mostly used for feeding arowana due to the belief it will enhance its color), while older culls, within their first year between 3" to 6" long (also called "Tosai"), are often sold as lower-grade, pond-quality koi.

The semirandomized result of the koi's reproductive process has both advantages and disadvantages for the breeder. While it requires diligent oversight to narrow down the favorable result the breeder wants, it also makes possible the development of new varieties of koi within relatively few generations.

Koi have been accidentally or deliberately released into the wild in every continent except Antarctica. They quickly revert to the natural coloration of common carp within a few generations. In many areas, they are considered an invasive species and pests. In the state of Queensland in Australia, they are considered noxious fish.[29]

Koi greatly increase the turbidity of the water because they are constantly stirring up the substrate. This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking, even by livestock. In some countries, koi have caused so much damage to waterways that vast amounts of money and effort have been spent trying to eradicate them, largely unsuccessfully.[30]

In many areas of North America, koi are introduced into the man-made "water hazards" and ponds on golf courses in order to keep water-born insect larvae under control through predation.